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bcarrigg90
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Posted Sun Oct 28, 2012, 2:12pm
Subject: dual boiler setup
 

I'm thinking of a way to have a dual boiler setup where the first boiler warms the water up partially or fully before it goes into the second boiler that heats it to brew temp.  Two small boilers could be used and still get good temp stability.  I'm trying to think of a way to hook the elements up, probably in series, so that when both elements are on, neither is supplied with full power so that I don't fry any wiring, but when the first boiler is up to temp, its element will shut off so the second one can have more power.  Thoughts?
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acasabia
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Posted Sun Oct 28, 2012, 2:17pm
Subject: Re: dual boiler setup
 

I think you have described most current dual boiler machines which feed the brew boiler from the steam boiler. Any 110v machine will alternate between the two heating elements. Usually you have the option to turn off one boiler or the other as well.

 
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JasonBrandtLewis
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Posted Sun Oct 28, 2012, 3:55pm
Subject: Re: dual boiler setup
 

And you would prefer making one at home from scratch, rather than buying any one of the many DB machines out there because . . .  ???

 
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bcarrigg90
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Posted Mon Oct 29, 2012, 3:57am
Subject: Re: dual boiler setup
 

How are the elements actually set up?  Is there a solid state relay that just switches from one to the other instead of just turning one on and off like it would in a single boiler setup?  

And I'm mostly just asking questions for theoretical reasons.  One day I want to build a dream machine after I've accrued several machines and their pare parts.  Custom is always cooler.  Even if its expensive.  Haha

This particular design that I'm thinking of would be a triple boiler.  One for steam, and two separate ones for the brew temp.  

Speaking of which, what determines the amount of steam pressure?  A large steam boiler?  Higher temperature?
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calblacksmith
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Posted Mon Oct 29, 2012, 4:37am
Subject: Re: dual boiler setup
 

higher temp= more pressure
larger volume= longer time at pressure.

 
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bcarrigg90
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Posted Mon Oct 29, 2012, 5:31am
Subject: Re: dual boiler setup
 

Seems logical enough.  So for the heating elements I was thinking of something like this.  The two elements on the brew side could be connected in series, with separate thermal switches or a pid/ssr setup that can switch each on individually.  so with both on, if they were 1000 watt elements, they would only get 500 watts each of power.  But once things are up to temp, they could have power if only one is on at a time.
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NobbyR
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Posted Mon Oct 29, 2012, 6:05am
Subject: Re: dual boiler setup
 

bcarrigg90 Said:

..., what determines the amount of steam pressure? ...

Posted October 29, 2012 link

Boiler pressure             Water temperature
(bar)                          (Fahrenheit)

1.0                               253

1.1                               255

1.2                               257

1.3                               259

 
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GVDub
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Posted Mon Oct 29, 2012, 6:53am
Subject: Re: dual boiler setup
 

bcarrigg90 Said:

Seems logical enough.  So for the heating elements I was thinking of something like this.  The two elements on the brew side could be connected in series, with separate thermal switches or a pid/ssr setup that can switch each on individually.  so with both on, if they were 1000 watt elements, they would only get 500 watts each of power.  But once things are up to temp, they could have power if only one is on at a time.

Posted October 29, 2012 link

This setup would take far longer to get to temp, and recovery time would be longer after making any drink that required both brewing and steaming. It would idle really nicely, though. Your proposed strategy seems as if it would deliver minimum power at the time maximum power was needed.

I love technology, but there are times when I question how it's applied early in the development curve. PID temperature control for a steam boiler is on of those things. Because of inertia, PIDs then to reduce power to "coast" into their set temperature. If the purpose of a steam boiler is to create steam in sufficient volume and with sufficient pressure to successfully turn out pitcher after pitcher of properly micro-foamed milk, you want things to get back to your set point as quicklly as possible, so using a pressure sensor under PID control would make more sense, or a pressurestat with as narrow as possible a dead band, as, assuming sufficient safety margin in the rating of your pressure vessel, slightly overshooting the temp/pressure in a steam boiler isn't anywhere near a problem.

Using a heat exchanger tube through the steam boiler to preheat brew water is an old trick at this point, I think, and a fine idea to keep recovery time jn the brew boiler to a minimum.
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bcarrigg90
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Location: cincinnati
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Grinder: Capresso Infinity - Modified
Drip: French press is as close as...
Posted Mon Oct 29, 2012, 8:32am
Subject: Re: dual boiler setup
 

I wasn't thinking of PID control on the steam boiler.  I guess this would actually be a three boiler machine.  I would just leave a normal mechanical thermostat on that boiler.

A heat exchanger makes a lot more sense than a preheating boiler and would probably be a lot simpler to implement.  My thinking was that if it held temperature well enough for a 25 second shot, the steam boiler would be the only one that would need to be on while pulling a shot.  If the brew boiler was at 200 and the preheat boiler was pumping in 200 water during the shot, it would be perfectly steady.  Then the brew boiler would just have to maintain temperature between shots, while the preheat boiler could work back up to temp.  

Another question:  Is there any type of high temperature pump that could be used after the boiler instead of before it?  

And what is this three way solenoid that commercial machines have to end up with a dry puck after a brew?
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GVDub
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Joined: 25 Jan 2008
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Location: Los Angeles, CA
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Roaster: Behmor 1600+
Posted Mon Oct 29, 2012, 8:56am
Subject: Re: dual boiler setup
 

Not sure just what advantage you'd be expecting to get having a pump after the boiler, and heat never increases the life of a component.

This thread over on Barista Exchange gives a pretty good summary of 3-way valves.
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